Summary: Defects in oocyte meiotic maturation are a major cause of human birth defects, miscarriage, and infertility. Many of the defining cellular, molecular, and biochemical features of meiotic maturation are deeply conserved. Over two decades, our research team established the nematode Caenorhabditis elegans as a genetic model for studying the control of meiotic maturation by intercellular signaling. In C. elegans, sperm signaling, via the major sperm protein (MSP), soma-germline interactions, and spatial cues regulate meiotic maturation. These signals ultimately result in the activation of maturation-promoting factor, the key regulator of meiotic maturation in most or all animals, which consists of the CDK1 protein kinase and the cyclin B regulatory subunit. Because late stage oocytes of most animals are transcriptionally quiescent, the regulation of protein translation is a key control point not only for meiotic maturation but also for additional aspects of oocyte development. In the prior funding period, we defined the central translational regulatory ribonucleoprotein (RNP) machine controlling meiotic maturation, which contains the conserved RNA-binding proteins (RBPs) LIN-41 and OMA-1/2 (referred to as the OMA proteins). LIN-41 and the OMA proteins act both in concert and antagonistically: LIN-41 inhibits CDK-1 activation and promotes oocyte growth and is inactivated in a spatially restricted manner to enable meiotic maturation, whereas the OMA proteins are required for CDK- 1 activation and meiotic maturation. We conducted extensive proteomic and genomic analyses to define additional protein components of the RNP machine and its mRNA targets. LIN-41?OMA RNP complexes not only arbitrate the spatial restriction of meiotic maturation, but they coordinate this key decision with oocyte growth and differentiation by controlling the translation of hundreds of important oogenic genes. The central questions are: (1) how LIN-41?OMA RNP complexes act as a switch to control meiotic maturation; and (2) how posttranslational mechanisms regulate the activity of LIN-41 to temporally and spatially control meiotic maturation and ensure its fidelity. Importantly, in mammals an OMA paralog is required for normal meiotic maturation, suggesting what we learn in C. elegans will provide general insights. Aim 1 will identify the molecular mechanisms and pathways LIN-41 and the OMA proteins regulate to control meiotic maturation. To achieve this goal we will: define the mechanism by which the OMA proteins control a translational repression- to-activation switch; and determine the mechanisms by which the RNPs remodel the oocyte proteome for meiotic maturation and the oocyte-to-embryo transition. Aim 2 will delineate the mechanisms by which LIN-41 is regulated to control meiotic maturation. To accomplish this goal, we will: determine how LIN-41 degradation might function as a timer to ensure the fidelity of the meiotic divisions; and illuminate the mechanism that inactivates LIN-41 as a translational repressor prior to its degradation. This basic research will broadly instruct our understanding of oogenesis and translational control.